SA589 Sames, SA589 Datasheet - Page 8

• Manufacturer Part Number: SA589
• Description: LD/DTMF SWITCHABLE DIALLERS WITH DEDICATED KEYS FOR 20 MEMORIES
• Manufacturer: Sames

SA589 FAMILY
Oscillator Circuit
This requires an external 560kHz ceramic resonator connected between OSC IN and OSC
OUT to provide a timing reference for all chip functions. No other components are required
or should be used.
The oscillator circuit is of the 'single pin' type. Internally, the OSC IN pin is connected to V
SS
and therefore the resonator may alternatively be connected externally between OSC OUT and
V
if desired.
SS
Please consult your resonator supplier who will recommend a suitable resonator type.
Tone Filtering
The spectral purity of the DTMF output is sufficient for most applications. However, where
lower distortion DTMF tones are required, an on-chip darlington pair is provided (accessible
via pins 7 & 8) for use in a low pass active filter.
Fig. 4 shows how a 2-pole Sallen and Key filter can be implemented. The typical component
values have been chosen to give a second order Butterworth response with a cut-off frequency
of about 3,5kHz and a nominal pass-band insertion loss of 0.5dB.
DTMF DIALLING
During DTMF dialling the MUTE output goes to logic '1' and remains there for the duration of
the tone transmission.
The IMP output remains low during tone transmission. The MF OUT output rises to its DC level
of 0.9 V
at the start of the tone transmission and is kept there between tone bursts. This is
DD
to avoid transients at the beginning and end of tone bursts.
The maximum rate at which tones are sent to line is 100ms on, followed by 100ms off (unless
specified otherwise). If keys are activated faster than this they are placed in a temporary store
and then sent to line at the maximum rate. Dialling from the LNR memory occurs at the
maximum rate.
If a key is held down for longer than the minimum Tone Burst period, the tone output will
continue until the key is released.
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